The present invention relates to an actuator for driving a printing wire or the like in a printing head, for example, and more particularly to a device for magnifying displacement of a piezoelectric element or the like as a driving source wherein expansion and contraction of the piezoelectric element is magnified through a rolling motion of a rolling member into a relatively large movement of the printing wire to carry out a printing operation of the printing wire. The present invention also relates to a method of producing such a device as mentioned above.
There are various known devices as mentioned above. For example, there is disclosed in Japanese Patent Laid-Open Publication No. 57-187980 a device for magnifying displacement of a piezoelectric element as shown in FIGS. 39(A) and 39(B). Referring to FIGS. 39(A) and 39(B) which show a rest condition and an operative condition of the device, respectively, a piezoelectric element 302 is fixed to a frame 300, and a rolling member 308 is connected through a pair of leaf springs 304 and 306 spaced a given distance from each other to the piezoelectric element 302 and the frame 300. As shown in FIG. 39(B), when the piezoelectric element 302 is expanded, the rolling member 308 is rolled about a connecting portion between the same and the leaf spring 306 by the moment generated at a connecting portion of the rolling member 308 and the leaf spring 304. Thus, the displacement of the piezoelectric element 302 is converted into a rolling motion of the rolling member 308.
However, such a conventional displacement magnifying device cannot exhibit a large magnification rate of displacement of the piezoelectric element 302 which is to be magnified and transmitted to the rolling member 308. Accordingly, in the case of driving a printing wire, it is necessary to lengthen the rolling member 308, so as to obtain a sufficient stroke of the printing wire. Such a large size and an increased mass of the rolling member 308 cause a problem in high-speed operation of the printing wire.
In the case that the displacement magnifying device as shown in FIGS. 39(A) and 39(B) is utilized in a printing head for a wire dot printer (not shown), for example, a printing wire is connected directly to one end of the rolling member 308 or indirectly such as through another member to the one end of the rolling member 308, thus constructing a printing unit. A plurality of a printing units of the number equal to that of the printing wires are installed in the printing head. Each printing unit includes the piezoelectric element 302, and lead wires extending from both electrodes of the piezoelectric element 302 are guided to a certain wiring board, and are connected to feeder lines formed on the wiring board by soldering or the like. However, in the connection of the lead wires, they tend to be tangled with each other, making the connecting operation difficult. Further, i is also difficult to recognize the polarity of the lead wires.
Furthermore, the plurality of printing units are usually located between two parallel base plates, and the frame 300 of each printing unit is fixed to the base plates by a suitable fixing means such as bolts directed parallel to a direction of displacement of the piezoelectric element 302. However, in fixing the frame 300 to the base plates, the frame 300 is expanded parallel to the direction of displacement of the piezoelectric element 302. Further, a fixed position of the frame 300 with respect to the direction parallel to the direction of displacement is slipped.